How do I...

[Sinful6]

...run an open dump? I have a THDP, ATR 2.5 exhaust with pitbull mufflers and a testpipe. Do I need to buy something else to let me bypass it and run an open dump?

 

[UNGN]

Terry houston sells a dump pipe that replaces the test pipe, or you can have one welded on yourself (to the test pipe)

There isn't much performance to be gained given your exhaust and I highly doubt you see even a .1 improvement with a dump.